In the field of integrated circuit fabrication, the drive to reduce circuit size has led to smaller electronic devices being packed with greater density on a common substrate. Examples of typical electronic devices used in integrated circuit applications include active devices, such as transistors, and passive devices, such as resistors and capacitors. Generally, the reliability of densely-packed electronic devices depends in part on providing sufficient electrical isolation between adjacent devices in the integrated circuit.
One common way to electrically isolate adjacent devices from each other is through the formation of local oxidization of silicon (“LOCOS”) structures. LOCOS structures are typically formed by depositing a non-oxidizable mask, such as silicon nitride (Si3N4), over a blank silicon wafer. The mask is patterned using photolithography, and then a film of silicon oxide (SiO2) is formed on the portions of the silicon surface exposed by the photolithographic process. The oxide film functions to electrically isolate devices formed over the portions of the substrate where the non-oxidizable mask remains.
Another common way to electrically isolate adjacent devices from each other is to form shallow trench isolation (“STI”) structures between the devices in the substrate. STI structures are typically formed by etching shallow trenches in the substrate between areas where electronic devices are to be formed, and then filling the trenches with an electrically insulating material, such as silicon oxide or another dielectric material. After the trenches are filled, the wafer surface is planarized by a chemical mechanical polish (“CMP”) process so that the insulating material remains in the trench, with its top surface level with that of the exposed silicon substrate. The “buried” insulating material provides electrical isolation between adjacent devices formed on or within the exposed substrate surface. A typical insulating material used to fill STI trenches is oxide, thin films of which are deposited using a high density plasma chemical vapor deposition (“HDP-CVD”) process.